I've stayed at the Quality Inn which is across Harbor Blvd. from Disneyland - Manchester Blvd. - East of Harbor, just South of I-5. (There is another Quality Inn nearby - Quality Inn Maingate).
The hotel wasn't particularly far from Disneyland itself, but it also wasn't the most direct route to get there.
I thought that the safety was reasonable, but no matter what, once you leave the park, you are in Southern California, so anything's possible.
In the end, I would recommend any woman who's alone to take a car rather than walk, just to play it safe.
Another option, although it will take up some of your time, is to park at Downtown Disney. You'll get a certain number of hours for free, and additional free hours with validation from any of the restaurants there. You can "cheat the system" by leaving midday, doing a u-turn, and pulling back into the parking lot with a new parking ticket to "reset" your free parking time.
This saves you some of the hassle of the tram to/from the Mickey and Friends structure, but since you only have one day, it may eat up more of your time than you would like when you move the car.
Whatever you do, be smart and enjoy your visit! :wave: